Note: Descriptions are shown in the official language in which they were submitted.
~L~L4Z8~6
"Method of and system for refrigerating a fluid to be cooled
down to a low temperature"
The present invention relates generally to a method of
and a system for refrigerating a fluid to be cooled down to a
low temperature ; more particularly it deals with and has es-
sentially for its subject matter a process of saving energy
and possibly initial capital expenditure and original cost in
a method of refrigerating at least one fluid to be cooled
down to a low temperature, lower than a presently preferred
value of -30C and in particular of a ~saseous fluid to be li~
quefied such as in particular a natural or synthetic gas as
for instance a methane-rich gas, as well as an apparatus for
carrying out this process. The invention is also directed to
the various applications and uses resulting from putting said
process and/or apparatus into practice as well as to the devi-
ces, assemblies, arrangements, equipments, plants, facilities
and like installations provided with such apparatus.
There are known methods of and systems for refrigerating
fluids to be cooled and in particular liquefying low tempera-
ture gases, wherein it is possible in particular by passing
the fluids through suitable heat exchangers to obtain the
condensation at high pressure and low temperature of natural
or synthetic gases and then the sub-cooling at high pressure
of the liquefied gases and afterwards the expansion in a val-
,~
',~
28~6
ve before recoverlng for instance the liquefied gases in acollecting vessel or storage tank at low pressure. It is al-
so known to use, for performing the refrigerating step, me-
thods wherein the refrigerating or cold-generating fluid
or ~luids are condensed at low temperat~re and high pressure
and wherein the liquid refrigerating fluid or fluids are
sub-cooled at very low temperature and at high pressure and
are then expanded in valves and vaporized at low pressure.
A main object of the present invention is to improve
this known state of the prior art in particular with a view
to decrease the power consumed by the compressors for the
refrigerating fluids with respect to a same amount of treat-
ed products, thereby reducing the cost of the treatment. For
this purpose the invention provides a process of saving ener-
gy and possibly initial cost in a method of refrigerating a-t
least one fluid to be cooled down to a low temperature, low-
er than a presently preferred value of -30C, such as in par-
ticular but not exclusively a method of liquefying a gas
through heat exchange with a single refrigerating fluid or
with a refrigerating fluid which is part of a system of seve-
ral refrigerating fluids evolving according to individual cy-
cles, respectively, combined into a cold-generating cascade
for instance of an incorporated type or equivalent to succes-
sive temperature drops ; the or each refrigerating fluid then
consists of a mixture of several different component substan-
ces and evolves accordin~ to a closed-loop cooling cycle whi~
undergoing therein successively : at least one compression in
the gaseous state, at least one preliminary cooling with at
least partial condensation or liquefaction of said mixture at
high pressure, at least one self-refrigeration with sub-cool-
ing of at least one liquid fraction through heat exchange in
counter-current relationship with the low pressure vapor o-
riginating from at least the same sub-cooled liquid fraction
of said same refrigerating fluid, at least one expansion of
at least said same ~raction down to a low pressure with at
least one conversion into said vapor which is then recompres-
sed. In other words during these known operating steps, said
2$~6
mixture or ~ractions ~hereol are cooled in one or several
heat exchangers in counter-current relationship with one or
portions of itself expanded down to one pressure or pressures
lower than said high pressure and then this mixture or said
fractions thereof are expanded in one or several expansion
members and are fed into the refrigerating heat exchanger or
exchangers.
The process of saving energy and cost according to the
invention is characterized in that it consists in reducing,
for a same amount of treated products, the power absorbed by
said compression by performing at least one or each aforesaid
expansion dynami~ly in order to produce an outer mechanical
work for instance likely to generate a continuous rotary mo-
-tion.
When the fluid to be cooled is a gas to be liquefied
flowing in particular in an open loop while being at least
partially liquefied at high pressure and wherein at least its
possibly or preferably previously sub-cooled liquid phaseis
expanded and then recovered or collected and for instance
stored in a static condition at low pressure, it is advanta-
geous that according to another characterizing ~eature of the
invention, said expansion be also effected dynamic~ly so as to
provide a similar outer mechanical work.
According to still another characterizing feature of the
invention, said outer mechanical work is reco~ered for gene-
rating either consumable converted energy or a useful techni-
cal effect.
According to still a further characterizing feature of
the invention, at least one or each aforesaid expansion is
carried out down to a pressure lower than at least 15 bars at
said high pressure.
According to still another characterizing fea-ture of the
invention, each aforesaid dynamic, motive power ~enerating
expansion is followed by an additional passive expansion
without any generation of outer work so as to keep the fluid
involved in a monophasic liquid condition, thereby avoiding
its vaporization at too low a pressure during said dynamic
~L4~346
expansion.
According to a further characterizing feature of the
invention, the nature or composition of at least one or each
aforesaid refrigerating fluid is adapted to or match~d with
the number of dynamic expansions.
The invention aims also at providing an apparatus for
carrying out said process, of the kind comprising : on the
one hand an in particular open circuit for the fluid to be
cooled, in particular for an aforesaid gas to be cooled,
comprising at least the following elements : at least one
passage-way for the fluid to be cooled within at least one
heat exchanger through which said refrigera~fluid is flow-
ing ; at least one liquid-phase or liquefied-gas expansion
member ; as well as, on the other hand, a closed circuit for
the refrigerating fluid, which is alone or is part of a sys-
tem of several distinct circuits of respectively different
refrigerating fluids, combined into a cold-generating cas-
cade or the like, said or each circuit including at least
the following elements : at least one compressor for gaseous
refrigerating fluid, at least one cooler and/or condenser and
at least said heat exchanger containing at least one flow
passage-way for the at least partially liquefied refrigera-
ting fluid and at least one passage-way for the vaporized re-
frigerating fluid extending in opposite direction ~ati~ toe~h
aforesaid flow passage-way while being connected at its up-
stream end with the downstream end of said flow passage~way
through the interposition of at least one member for expand-
ing at least one fraction of the liquid phase of said refri-
gerating fluid and, at its downstream end, to the suction si-
de of said compressor.
According to the inven-tion, this apparatus is characte-
rized in that at least one or each aforesaid expansion member
consists of at least one driven cryogenic turbo-machine ha-
ving at least one hydraulic turbine or operating with a prac-
tically incompressible working fluid.
'' 31 ~ ~Z~
According to another characterizing feature of the in-
vention, the fluid outlet of at least one or each aforesaid
turbo-machine is connected to an addi-tional expansion valve.
According to still a ~urther characterizing feature of
the invention, at least one or each aforesaid turbo-machine
has its shaft connected to at least one electric-power or ~
work generating machine. `
The invention thus defined brings about a substantial
technical improvement because it offers the main following
advantages :
- a substantial reduction in the compression power re-
quired (i.e. the power absorbed by the compressors for the
refrigerating fluids) for a same amount of liquefied fluid :
this gain in power may reach for instance about 10 % in the
case of the liquefaction of the natural gas in particular
rich in methane ;
- a possible energy recovery by using the mechanical
energy provided by the cryogenic expansion hydraulic turbi-
nes for driving either electric-power generating machines or
other auxiliary rotary machines ; this recovered energy
may be for instance of up to about 5 % of the energy consum-
ed by said compressors.
It results therefrom that the invention makes it possi-
ble to achieve a total energy saving which may for instance
be up to about 15 % of the total energy input absorbed by
the compressors for the refrigerating fluids.
The invention is applicable to any system of ~luid re-
frigeration and its criterion of use is essentially condi-
tioned by the energy-saving policy or economy of the country
where it is worked because its interest mainly depends on
the local energy cost and ~or instance in particular on the
price of e~ergy supply. Thus according to the relative value
of such a cost, i.e. if the energy supply is relatively ex-
pensive, it may be advantageous to use cryogenic expansion
hydraulic turbines even at less lower temperatures.
;28~6
It should be pointed out in this connection that an
expansion turbine is the more advantageous than an expansion
valve as the temperature of the fluid to be expanded is low-
er before its expansion. The gain in refrigerating fluid
compression power input, provided by the use of hydraulic
expansion turbines, is the more better as the efficiency of
the refrigeration cycle is worse. The refrigeration cycle
should work with relatively high pressure differentials.
The heat exchangers and/or condensers used may be of
any type such as in particular of the coiled type, of the
plate type,ofthe finned-tube type and so on.
The invention will be better understood and further ob-
jects, characterizing features, details and advantages the-
reof will appear more clearly as the following explanatory
description proceeds with reference to the accompanying dia-
grammatic drawings given by way of non-limiting examples on-
ly illustrating several presently preferred specific embodi-
ments of the invention and wherein :
~ Figure 1 shows a first embodiment of a system of li-
quefying a for instance natural gas by means of one singlerefrigera-ting fluid undergoing one single expansion ;
- Figure 2 illuStrates an alternative embodiment or mo-
dification of the foregoing system, with phase separation
and double expansion of the refrigerati.ng fluid ;
- Figure 3 shows another embodiment with the use of two
refrigerating cycles for a main and an auxiliary fluid, res-
pectively, combined into a cold-generating cascade by a
common heat exchanger, with a single expansion of the auxi-
liary refrigerating fluid and pre-cooling of the gas to be
liquefied ;
- Figure 4 shows still another embodiment with two re-
frigerating cycles for a main and an a~xiliary fluid, res-
pectively, with multiple-stage compression and double expan-
sion of the auxiliary refrigerating fluid and with two heat
exchangers connected in series for combining both cycles and
three times expansion of the main refrigerating fluid ; and
46
- Figure 5 illustra-tes still another embodiment compri-
sing a preliminary partial double liquefaction of the single
refrigerating fluid within an auxiliary heat exchangin~ co-
lumn.
In the various figures o~ the drawings, the same refe-
rence numerals are used to designate like or similar ele-
ments or parts and the numerical pressure values stated by
way of example are absolute pressures.
According to the examplary embodiment shown on Figure 1,
the open circuit of cooled fluid in particular of for instan-
ce nature gas GN to be liquefied is generally designated by
the reference numeral 1 whereas the closed circuit of main
refrigerating fluid is generally denoted by the reference nu-
meral 2, both circuits being thermally combined through the
agency of at least one common cryogenic heat exchanger 3 for
liquefying the gaseous fluid.
The open circuit 1 comprises an inlet duct 4 leading in-
to the heat exchanger 3 and connected to at least one inner
passage-way of this exchanger which consists for instance of
a nest, cluster or the like bundle of coiled tubes 5 the out-
let of which is connected through a duct 6 to the inlet of a
cryogenic hydraulic expansion turbine 7 the outlet of which
communicates through a pipe-line 8 with a vessel or like
tank 9 for preserving or storing for instance liquefied natu-
ral gas GNL. An expansion valve 10 may advantageously but op-
tionally be inserted into the pipe-line 8 between the turbine
7 and the tank 9. The powered output drive sha~t of the tur-
bine 7 may advantageously but optionally be coupled to a rota-
ry machine 11 to be driven which is for instance an electric
power generator (thus ~orming an electric power generating
set with the turbine 7).
The closed circuit 2 (bounded and symbo~ lY shown by a
box or rectangle drawn in chain-dotted discontinuous lines)
contains a refrigerating fluid consisting of a mixture of se-
veral components at least a major part of which consists ad-
vantageously of hydrocarbons.
9L~4~8~6
This circuit 2 successively comprises in the direction
of flow of the refrigerating fluid : at least one compressor
12 for the refrigerating fluid in the gaseous state, having
for instance two stages, namely a low pressure stage 12a and
a high pressure stage 12b driven each one either separately
by an individual prime mover or together jointly by a common
motor while having then their respective shafts coupled me-
chanically. This compressor is adapted to compress the refri-
gerating fluid in the gaseous state and the compressed fluid
outlet or delivery port of the low pressure stage 12a is
connected to the suction port of the high pressure stage 12b
through an intermediate or inter-stage cooler 13 the cooling
fluid of which is advantageously supplied from the outside
and consists for instance of water or air. The outlet or de-
livery port of the high pressure compression stage 12b is
connected to a corresponding inlet of the heat exchanger 3
through at least one final or after-cooler 15 and at least
one condenser 16. The after-cooler 15 is advantageously of
the same kind as the inter-stage cooler 13, i.e. with a
cooling fluid supplied from the outside and consisting for
instance of water or air whereas the condenser 16 has its
cooling ~luid also supplied from the outside and consisting
for instance of propane or propylene. More specifically at
the inlet into the heat exchanger 3, the pipe-line 14 is con-
nected to the upstream end of at least one inner flow passage~
way 17 extending generally in the same direction as the flow
passage-way 5 and having i~ downstream end connected through
a duct 18 issuing from the heat exchanger 3 to the inlet of
a cryogenic hydraulic turbine or the like 19 located for ins-
tance outside of the heat exohanger 3. The outlet of thisturbine 19 is connected thi~ough a duct 20 to a distributing
system placed inside of the heat exchanger 3 and consisting
either of at least one confined passage-way extending in at
least approximately parallel relation to the flow passage-ways
5 and 17, from the respecti~e downstream ends to the respec-
gL~428~1~
tive upstream ends thereof, or of a jet-producing spray de-
vice or the like 21 communicating with the inner space of
the casing or shell of the heat exchanger 3 and opening di-
rectly into that space, so that the sprayed fluid would
flow while keeping vaporizing in said direction about the
flow passage-ways 5 and 17 so as to stream thereabout in
direct contact therewith.
At least one additional expansion valve 22 may be in-
serted into the pipe-line 20 between the outlet of the tur-
bine 19 and the corresponding inlet of the heat exchanger 3.The output drive shaft of the turbine 19 may possibly be
coupled mechanically with the drive shaft of a rotary machi-
` ne 23 for instance of the same kind as the rotary machine 11and consisting in particular either of an electric power ge-
nerator or of any work-producing machine.
The operation of this system is then the following :
the for instance natural gas GN to be liquefied is fed into
the duct 4 at an absolute high pressure for instance of
about 40 bars and at a temperature for instance of about
-35~C. This gas flows through the flow passage-way 5 of the
heat exchanger 3 while being therein in heat exchange with
said refrigerating fluid so as to be successively cooled
down until liquefaction and then sub-cooled, so as to leave
the heat exchanger 3 still at a high pressure through the
duct 6 while being at a temperature for instance of about
-150C. The liquefied gas then flows through the hydraulic
turbine 7 and expands therein down to a low pressure for ins-
tance of about 3 bars while therein producing an outer work
driving the turbine 7 in a continuous rotary motion, which
turbine may in turn possibly drive a rotary machine 11 mecha-
nically to provide a useful technical effect. When issuing
from the turbine 7, this expanded fluid possibly undergoes &n
additional expansion through an expansion valve 10 so as to
be for instance eventually recovered or collected and stored
in the liquid condition GNL in the tank 9.
1 0
~28~;
As to the operating cycle of the refrigerating fluid,
the latter is drawn in the wholly vaporized state at a low
pressure for instance of 2.7 bars in a temperature ~or ins-
tance of about -38C into the low pressure compression sta-
ge 12a of the compressor 12 wherefrom it is discharged at
an intermediate pressure through the inter-stage cooler 13
and then drawn in~o the high pressure compression stage 12b
of -the same compressor which then delivers it still in the
gaseous state at a high pressure for instance of about 40
bars into the pipe-line 14 successively through the after-
cooler 15 and then through the condenser 16 where the re~ri-
gerating fluid is condensed partially orwhoIly still at the
same aforesaid high pressure and at a temperature for ins-
tance of about -35C. It then enters the.flo.wipassage-way 17
of the heat exchanger 3 where it is in heat exchange with a
vaporized portion of itself, so as to be further cooled the-
rein possibly until total liquefaction (if same has not fully
taken place within the condenser 16) and then to be sub-cool-
ed therein in the liquid condition down to a temperature for
instance of about -150C at a pressure of about 38 bars for
being then fed through the pipe-line 18 into the hydraulic
turbine 19 where it expands down to a low pressure for instan-
ce of about 3 bars at a temperature fo:r instance of about
-150C and then returns through the pipe-line 20 into the heat ..
exchanger 3 9 possibly after having flown through the valve 22
to undergo an additional expansion therein. The expansion
within the turbine 19 would generate or sustain the continuous
rotary motion thereof with possible attendant driving of the
rotary machine 23. The expanded refrigerating fluid is then
distributed through the for instance jet-producing spray mem-
ber 21 inside of the casing or shell of the exchanger 3 and
this refrigerating fluid is flowing while keeping vaporizing
within that shell through the heat exchanger in counter-cur-
rent relationship with respect to the flow passage-wa~s 5 and
17 which it strongly cools while streaming thereabout (there-
by inducing, within these flow passage-ways, the total lique-
faction of the fluids contained therein and then the respec-
tive sub-cooling thereof). Th~ vaporized refrigerating fluid
issues from the heat exchanger 3 through the outlet port 24
at said low pressure of 2.7 bars and at the temperature of
-38C to flow back through the duct 25 to the suction port
of the low pressure stage 12a of the compressor 12, so as
to resume the cycle which is thus repeated as long as the
circuit 1 is fed with a flow rate of gas to be liquefied.
Since owing to the invention the expansion of the liquefied
gas within the turbine 7 enables the gas to be cooled down
substantially more than through a simple valve a this makes
it possible to reduce the cooling capacity or power of the
heat exchanger 3 hence also the required input power absorb-
ed by the compressor 12~ thus making the plant less expensi-
ve. Due to the replacement according to the invention of the
usual expansion v~ves by hydraulic expansion turbines, the
heavy energy loss within such valves in view of the great
pressure differential in the expansion is thus removed so
that the system according to Figure 1 which is very advanta-
geous on account of its simplici-ty becomes of particular in-
terest owing to its high performance.
The system shown on Figure 2 differs from the one illus-
trated in Figure 1 by the more elaborated cons-truction of the
circuit and operating cycle 2 of the refrigerating fluid. The
heat exchanger 3 is split here into two parts or sections 3a
and 3b which instead of being part of a same apparatus or
common assembly may consist of separate units communica~ngwith
or connected in series to each other. In the section 3a is
carried out the liquefaction of the fluids involved and in
particular of the gas to be lique~ied as well as of the ga-
seous phase of the refrigerating fluid whereas in the section
3b is effected the sub-cooling of the ~luids respectively
lique~ied in the section 3a.
Between the condenser ~6 and the section 3a of the heat
exchanger 3 is inserted a phase separator 26 connected to the
~28416
outlet of the condenser 16 whereas the flow passage-way of
Figure 1 is here substituted for by two flow passage-ways
17a and 17b, respectively, extending in substantially paral-
lel relationship and the first one of which extends succes-
sively within the sections 3a and 3b OI the heat exchanger 3
whereas the other one 17b extends within the section 3a only.
The flow passage-way 17a has its upstream end connected
through the pipe-line 14a to the vapor phase collecting spa-
ce of -the phase separator 26 whereas the flow passage-way 17b
has its upstream end connected through the pipe-line 14b to
the liquid phase collecting space of the phase separator 26.
The downstream end of the flow passage-way 17a is connected
through a pipe-line 18a to the inlet of the cryogenic hydrau-
lic expansion turbine 19a (possibly coupled with its shaft
mechanically to a rotary machine 23a~ the outlet of which is
connected through the pipe-line 20a (possibly through an ad-
ditional expansion valve 22a) to an (in particular jet-produ-
cing spray) distribution member 21a positioned at the corres-
ponding end of the section 3b of the heat exchanger 3. The
do~,mstream end of the flow passage-way 17b is connected
through the pipe-line 18b to the cryogenic hydraulic expansion
turbine 19b (possibly coupled with its shaft mechanically to
a rotary machine 23b) the outlet of which is connected through
the pipe-line 20b (possibly through an additional e~pansion -
valve 22b) to the (for instance jet-producing spray) distri-
bution member 21b placed at an intermediate position within
-the heat exchanger 3 substantially at that end which is com-
mon -~o both adjacent sec~ions 3a and 3b thereof.
This system operates as follows:
The natural gas GN for instance at a temperature of
about -35C and at a pressure for instance of about 45 bars
enters in the gaseous state the segment of the flow passage-
way 5 located within the section 3a of the heat exchanger 3
and is liquefied therein and afterwards this liquefied gas is
sub-cooled in that portion of the flow passage-way 5 which is
~4~6
located within the section 3b of the heat exchanger 3 where-
from it issues at a temperature for lnstance of -160C and
at an absolute pressure of 42 bars for being then successi-
vely expanded and stored as described with reference to
F1gure 1.
The refrigerating fluid, compressed at a high pressure,
is partially condensed in the condenser 16 for instance at
the temperature of -35C and at a pressure of 40 bars into a
mixture of gaseous and liquid phases, respectively9 which
are separated from each other in the separator 26. The ga-
seous phase is fed by the duct 14a into the segment of the
flow passage-way 17a located in the section ~a of the heat
exchanger 3 to be liquefied therein and then this liquefied
fraction is sub-cooled in that portion of the flow passage-
way 17a which is placed in the section 3b of the heat ex-
changer 3, wherefrom this sub-cooled fraction issues through
the pipe~line 18a at a temperature for instance of about
-160C and at a pressure for instance of about 38 bars to
thereafter flow through the hydraulic turbine 19a while ex-
panding therein. This expansion (which induces a continuousrotary motion of the turbine and poss:ibly of the rotary ma-
chine 23a) has cooled that fraction down to a temperature
for instance of about -163C thereby Lowering its pressure
for instance down to about 3.2 bars and this expanded frac- -
tion is fed by the pipe-line 20a (possibly after an addi-
tional expansion in the valve 22a) to the distributing mem-
ber 21a wherein the expanded fraction is sprayed for instan-
ce. The refrigerating fluid thus sprayed flows ~or instance
inside of the casing or shell of the heat exchanger 3 while
keeping vaporizing and streaming about the flow passage-ways
5, 17a and 17b in counter-current relation to the fluids
carried in these flow passage-ways, respectively. The frac-
tion of liquid refrigerating fluid, coming f~om the separa-
tor ~6, is fed through the duct 14b into the flow passage-
way 17b of the heat exchanger 3 to be sub-cooled therein
down to a temperature for instance of about -120C at a
8~ Ei
pressure for instance of about 38 bars and it leaves the
heat exchanger 3 through the duct 18b t~ thereafter flow
through the hydraulic turbine 19b while expanding therein
(thus inducing the continuous rotary motion of the turbine
and possibly of the driven rotary machine 23b). This expan-
sion has thus cooled this fraction down to a temperature
for instance of about -123C thereby lowering its pressure
for instance down to about 3.0 bars and the expanded fluid
is fed through the duct 20b to the distributing member 21b
for being for instance sprayed therein inside of the shell
of the section 3a of the heat exchanger 3 wherein it keeps
vaporizing. This vaporized ~raction of the re~rigerating
fluid mixes with the vaporized fraction of the refrigerating
fluid coming from the section 3b of the heat exchanger to
flow for instance while streaming about the three flow pas-
sage-ways 5, 17a and 17b in counter-current direction with
respect to the directions of flow of the respective fluids
in these three flow passage-ways. Such a direct contact bet-
ween the vaporized refrigerating fluid and said flow passa-
ge-ways will resu~ in a strong heat exchange therebetween,
thus achieving on the one hand the strong sub-cooling of the
li~uefied gas and of the liquefied refrigerating fluid flow-
ing in the corresponding portions of the flow passage-ways 5
and 17a, respectively, located in the section 3b of the heat
exchange~ 3 and on the other hand the liquefaction of these
fluids in the corresponding portions of the flow passage-ways
5 and 17a positioned in the section 3a of the heat exchanger
as well as the sub-cooling of the liquid refrigerating fluid
oirculating in the flow passage-way 17b in the same section
3a of the exchanger. The total vaporized refrigerating fluid
issuing from the heat exchanger 3 through the outlet port 24
and the duct 25 at the temperature of -38C and at the pres-
sure of 2.7 bars is drawn in again by the compressor 12 with
a view to repeating the refrigerating cycle.
~28~6
The system shown in Figure 3 dlffers mainly from that
shown in Figure 2 on the one hand by a previous cooling of
the gas to be liquefied and on the other hand by the use of
two distinct cycles of refrigerating flui~s, namely a cycle
of main or light refrigerating fluid 2 and a cycle of auxi-
liary or heavy refrigerating fluid 3, consisting of a mix-
ture of components and combined into a kind of cold-genera-
ting incorporated cascade by means of a condenser 16' form-
ing a cryogenic heat exchanger common to both refrigeration
cycles 2 and 3 between which it thus provides a thermal
connection.
The circuit 1 of gas to be liquefied thus comprises a
cryogenic heat exchanger 27 for previous refrigeration of
the gas to be processed and common to both circuits of gas
to be liquefied 1 and of main or light refrigerating fluid
2. This ex~hanger 27 is for instance of the plate type and
includes passage-ways 28, 29 inserted respectively in the
duct 4 before the heat exchanger 3 and in the duct 25 bet-
ween the outlet 24 of the heat exchanger 3 and the low pres-
20 sure suction port of compressor 12. In the duct 4 betweenthe outlet of the exchanger 27 and the inlet of the exchan-
ger 3 may also be inserted a gas treating apparatus 30 (ef-
fecting for instance the removal of heavy components there-
from).
The circuit 1 then operates as follows :
the gas to be liquefied GN, entering the duct 4 at a
temperature for instance of abou`t ~20C and at an absolute
pressure for instance of about 46 bars flows through the
passage-way 28 of the heat exchanger 27 to be preliminarily
30 cooled and possibly partially condensed therein through heat
exchange with the main refrigerating fluid circulating in
the passage-way 29. When leaving the exchanger 27, the gas
flows through the treating apparatus 30 wherefrom it issues
at a temperature for instance of about -50C and at a pres~
sure for instance of about 45 bars to thereafter flow through
1G
~ 8~6
the flow passage-way 5 of the heat exchanger ~ to be fully
liquefied and then sub-cooled therein down to a temperature
for lnstance o~ about -158C and at a pressure for instance
of about 42 bars. This liquefied gas is thereafter expanded
and then stored as previously described for instance at
-158.5C and 1.10 bar.
In the cycle 2 of the main or light refrigerating
fluid, the condenser 16' forming a cryogenic heat exchanger
advantageously of the plate type comprises at least one flow
passage-way 31 inserted in the duct 14 between the outlet of
the after cooler 15 and the inlet of phase separator 26.
This cycle 2 then operates as follows :
When issuing from the after-cooler 15, the main refri-
gerating fluid is for instance at a temperature of about
+30C and at a pressure of about 41 bars and flows through
the flow passage-way 31 of the cryogenic exchanger 16' to be
partially condensed therein through heat exchange with the
auxiliary or heavy refrigerating fluid from the refrigera-
tion cycle 3. The main or light refrigerating fluid thus
partially condensed for instance at a temperature of about
-50C and at a pressure of about 40 bars will then undergo a
phase separation within the separator 26. I-~ liquid phase
sub-cooled within the heat exchanger 3 for instance down to
a temperature of about -130C and at a pressure for instance
of about 38 bars is expanded as mentioned hereinbefore the-
reby having its temperature lowered for instance to about
-133C and its pressure lowered to 3.5 bars and then keeps
vaporizing in the heat exchanger 3 whereas the vapor phase of
the main refrigerating fluid, successively liquefied and then
sub-cooled in the heat exchanger 3 ~or instance down to a
temperature of about -158C a~datapressure of about 36 bars
is expanded as aforesaid thus having its temperature lowered
for instance to about -163C and its pressure lowered for
instance to about 3.7 bars and it keeps vaporizing in the
heat exchanger 3. The total vaporized main refrigerating fluid
~Z~6
issuing from the heat exchanger 3 through the outlet port
24 for instance at a temperature of about -60~C and at a
pressure o~ about 3.2 bars flows through the passage-way
29 in counter-current relation to the direction of flow of
the gas to be liquefied in the passage-way 28 for cooling
the latter therein through heat exchange. The main refrige-
rating fluid thus reheated in the heat exchanger 27 leaves
the latter for instance at a temperature of about ~ 7C at
a low pressure of about 3 bars to be drawn in again through
the pipe-line 25 by the compressor 12.
The closed circuit 3 of auxiliary or heavy refrigera-
ting ~luid successively comprises in the direction of flow
of the latter : a compressor set 32 consisting of two stages
or compressors, namely a low pressure stage or compressor
32a and a high pressure stage or compressor 32b. The inter-
mediate pressure outlet or delivery port of the first com-
pressor 32a is connected to a duct 33 connected to the inlet
of a condenser 34 which advantageously is of the type opera-
ting with an outer coolant consisting for instance of water
or air. The outlet of the condenser 34 is connected to a
phase separator 35 the gaseous phase collecting ~ ace o~
which is connected through a pipe-line 36 to the suction port
of the second compressor 32b the outlet or discharge port of
which is connected through a pipe-line 37 to a condenser 38
which is advantageously of the type operating with an outer
cooling medium consisting for instance of water or air. The
liquid phase collecting space of the phase separator 35 is
connected by a duct 39 through a circulating ~nd accelera-
ting pump 40 to the delivery duct 37 of the second compres-
30 sor 32b at a branch point 41 located between the latter andthe condenser 38.
The auxiliary refrigerating fluid outlet of the conden-
ser 38 is connected to the upstream end o~ at least one flow
passage-way 42 contained in the heat exchanger 16' and the
outlet of which is connected through a pipe-line 43 to the
inlet of a cryogenic hydraulic e~pansion turbine 44 which is
1 ~3
outside of the heat exchanger 16'. The shaft ~f this hydrau-
lic turbine 44 is possibly coupled mechanically to a rotary
machine 45. The outlet of the hydraulic -turbine ~4 is con-
nected through a pipe-line 46 to the upstream end of at least
one passage-way 47 for the auxiliary refrigerating fluid in-
side of the heat exchanger 161, which is for instance of the
plate construction type. The flow lines and passage-ways 31,
42 and 47 extend in generally parallel relation to a same
direction while being in mutual heat exchange with each other.
10 The downstream end of the passage-way 47 is connec-ted through
the outlet 48 of the heat exchanger 16' by a pipe-line 49 to
the suction port of the first compressor 32a.
The operation of this cycle 3 of auxiliary or heav~ re-
frigerating fluid is then the following : the auxiliary re-
frigerating fluid is sucked in the gaseous state for instance
at a temperature of about +25C and at a low pressure of
about 3 bars by the first compressor 32a which discharges i-t
atan intermediate pressure throlgh the condenser 34 where the
compressed auxiliary refrigerating fluid partially condenses
into a mixture of gaseous and liquid phases, respectively,
which are thereafter separated within the phase separator 35.
The gaseous phase, which is for instance at a temperature of
about +30C and at an in-termediate pressure of` about 15 bars,
is drawn in by the second compressor 3Zb to be delivered at --
high pressure into the duct 37. The liquid phase at said
same intermediate pressure is drawn in by the pump 40 which
raises its pressure up to the delivery pressure of the
second compressor 32b and forwards this compressed li~uid
phase until it joins at 41 the gaseous refrigerating fluid
discharged at high pressure into the pipe-line 37. This mix-
ture of high pressure gaseous and liquid phases, respective-
ly, then flows through the condenser 38 where the auxiliary
refrigerating fluid is fully condensed and leaves this con-
denser for instance at a temperature of about +30C and at a
pressure of about 25 bars. The liquid refrigerating ~luid
19
~28416
then flows through the flow passage-way 42 of the heat ex-
changer 16' where it is sub-cooled for instance down to a
temperature of about -50C and at a pressure of about 23
bars through heat exchange with a vaporized fraction o~ it-
self. This refrigerating fluid thus sub-cooled then flows
through the hydraulic turbine 44 to be expanded therein
(thus inducing a continuous rotary motion of this turbine
and possibly the attendant drive of the rotary machine 45),
thereby having its temperature lowered ~or instance to about
-53~C and its pressure lowered to about 3.3 bars. When iS6U
ing from the turbine 44, the expanded refrigerating fluid
may optionally be expanded additionally by flowing through
an expansion valve 50 possibly inserted in the duct 46 and
thereafter flows through the passage-way 47 to keep vapori-
zing at low pressure by circulating therein in counter-cur-
rent relation to the respective directions of flow of the
fluids in the flow passage-ways 31 and 42. The vaporized au-
xiliary refrigerating fluid thus provides through heat ex-
change on the one hand for the cooling of the main or light
refrigerating fluid in the flow passage-way 31 until its
partial condensing and on the other hand for the sub-cooling
of the heavy or auxiliary liquid refrigerating fluid circu-
lating in the flow passage-way 42. At its egress 48 from the
heat exchanger 16', the vaporized auxiliary refrigerating
fluid is for instance at a temperature of about ~25C and at
a pressure of about 3 bars at which it is drawn in again in
the gaseous state by the first compressor 32a for causing
the refrigerating cycle 3 to be repeated.
~y way of mere illustration, a comparison o~ the res-
pective performances of a system according to the invention
as shown on Figure 3 and of a system according to the prior
art using a circuit diagram similar to that shown on Figure
3 but wherein the expansions are made in valves, is given
hereinafter.
In both cases considered (invention and prior art), the
natural gas to be liquefied is available in the following
conditlons :
- temperature : 20C
absolute pressure : 45 bars
- mass flow rate : 181,500 kg/h
- chemical composition in % in weight :
methane : 79.56
- ethane : 9.95
- propane : 7.29
- isobutane : 1.60
- normal butane : 1.60
At the outlet of the expansion member the liquefied gas
is obtained in -the following conditions :
- temperature : -158.5C
- absolute pressure : 3 bars
- mass flow rate : 181,500 kg/h
- chemical composition : identical with that of natural
gas.
The liquid natural gas is then stored in a tank at an
absolute pressure of about 1.10 bar.
The active surfaces of the heat exchangers 16', 27, 3a
and 3b are identical and the values of the ratios of the
amounts of heat exchang~ at the main or average temperature -
approaches are the following, respectively :
- 8,500,000 kcal/h/C for the heat exchanger 16' ;
- 1,450,000 kcal/h/C for the heat exchanger 27 ;
- 9,200,000 kcal/h/C for the heat exchanger 3a ;
- 1,700,000 kcal/h/C for the heat exchanger 3b.
The comparison of the respective performances of both
aforesaid cases is given by the numerical data of the fol-
lowing table :
.42~3~1L6
Table 1
. ~ . . .
Prior art accor
Invention ding to Figure
Performancesaccording without turbine
to Figure 3 (expansion in
. _ . valves)
Main cycle ?
Characteristics of refrigera-
ting fluid:
Total mass flow rate in kg/h : 339, 320 352, 850
Composition in % by weight:
- nitrogen 7 . 24 8 . 37
- methane 26 . 91 26 . 51
- ethane 49 . 79 51 . 84
- propane 16 . o6 1 3 . 27
Power of compressors 12 in kW: 33,737 35,283
. _
. ..... ......
Auxiliary cycle 3
Total mass flow rate in kg/h: 41 6 , 01 3 431, 270
20 Composition in % by weight:
- methane 0. 78 1 .18
- ethane 32 . 66 33 .11
- propane 24.48 25.89
~ isobutane . 21. 04 19 . 91
- normal butane 21.04 19.91
Power o~ compressors 32 in kW: 16,961 18,463
_~. ............ _ .... _
Power of turbines in kW
- turbine 7 350 O
- turbine 19a 92 O
3o - turbine 19b325 0
- turbine 44 290 0
Total power of turbines in kW: 1,057 0
_ _. .
... ... __ _ . . ._ _._ _ __ . .... . .... _ _
Total power of compressors in kW 50,698 ._
It is thus found that the gain in total power of the
compressors is of 3,048 kW or about 6 % of the total power of
the compressors. The total power which may posslbly be reco-
vered as mechanical energy on the shafts of the expansion
turbines is 1,057 kW or about 2 % of the total compression
power.
The expansion of the liquefied natural gas GNL is car-
ried out in the turbine 7 only. The respective expansions of
the main and auxiliary refrigerating fluids are carried out
in two steps, namely :
- a monophasic expansion in each expansion turbine 19a,
19b, 44 ;
- a diphasic expansion in each valve 22a, 22b, 50 loca-
ted downstream.
The next absolute pressure reductions are obtained
through the expansions carried out according to the circuit
diagram of Figure 3 :
- liquefied natural gas GNL expanded from 42 bars to 3
bars in the turbine 7 ;
- main refrigerating fluid expanded from 36 bars to 6.2
bars in the turbine 19a ;
~ main refrigerating fluid expanded from 6.2 bars to
3.7 bars in the valve 22a ;
- main refrigerating fluid expanded from 38 bars to 7
bars in the turbine 19b ;
- main refrigerating fluid expanded from 7 bars to 3.5
bars in the valve 22b ;
- auxiliary refrigerating fluid expanded from 23 bars to
4.3 bars in the turbine 44 ;
- auxiliary refrigerating fluid expanded from 4.3 bars
to 3.3 bars in the valve 50.
In both cases considered o~ the invention and of the
prior art, respectively, the operating conditions are the sa-
me except for the following :
~4~8~6
TabIe 2
__ .
Conditions Invention Prior art
_
Temperature of -the liquefied natural
gas at 6 and of the main refrigera-
ting fluid at 18a, in C -158 -160
Absolute pressure of the auxiliary
refrigerating fluid at the outlet of
38, in bars 25 26~4
Absolute pressure of the auxiliary
refrigerating fluid at 43, in bars 23 24.4
The gains in power achieved due to the use of the turbi-
nes are stated in the numerical data of the following table :
Table 3
_ Expansion tem- Gain in refrigera-
Turbine n Turbine po- perature, in ting fluid compres-
wer in C sion power, ln kW ..
7 350 -1581,403
19a 92 -158 380
19b 325 -130 982
44 290 - 50 283
. ._ __ _ _ _ _
Total sum 1,057 . 3,048
It is seen that the use of a hydraulic expansion turbine
is the more advantageous as the temperature is lower.
24
2B~6
In the typical examplary embodiment according to Figure
3, the required total power of the compressors 12 and 32 for
the main or light and auxiliary or heavy refrigerating fluids,
respectively, thus has the following values :
- without using the turbines 7, 19a, 19b and 44 :
53,746 kW ;
- when using said turbines : 50,698 kW.
Therefore the use of said hydraulic expansion turbines
makes it possible to achieve a total gain of 3,048 kW in the
power of the compressors for the refrigerating fluids in the
typical example considered whereas the total mechanical ef-
fective power which may be recovered on the turbine shafts
whould amount to 1,057 kW.
The system according to Figure 4 relates to a more ela-
borated structure of both cycles of the main or light refri-
gerating fluid 2 and the auxiliary or heavy refrigerating
fluid 3, respectively. The condensing heat exchanger 16` of
Figure 3 has been replaced here by two distinct units 16'a
and 16'b forming heat exchangers for instance of the plate
construction type, respectively, and communicating with ~ c~
nected in series to each other, which may be either distinct
units or units integrated into a same common heat exchanger
body of which they form two successive parts.
In the cycle 2 of the main or light re~rigerating fluid
the outlet o~ the after-cooler 15 is connected through a duct
14 to the upstream end of at least one flow passage-way 31a
contained in a first condensing heat exchanger 16'a and the
downstream end of this flow passage-way 31a is connected at
the outlet of this exchanger 16'a to a phase separator 51.
The liquid phase collecting space of this separator is con-
nected through a pipe-line 52 to the upstream end of at least
one flow passage-way 53 contained in the heat exchanger 27
and extending therein in substantial parallel relation to the
general common direction of the passage-ways 28 and 29. The
downstream end of the flow pas~age-way 53 is connected through
a pipe~line 54 to the $nlet of a hydraulic expansion turbine
28~6
55 (the shaft of which is possibly coupled mechanically to a
rotary machine 56) the outlet of which is connected by a pi-
pe-line 57, possibly through an additional expansion valve
58 to the duct 25 at a branch point 59 located between the
outlet port 24 of the heat exchanger 3 and the corresponding
inlet port of the heat exchanger 27.
The gaseous phase collecting space of the phase separa-
tor 51 is connected through a pipe-line 60 to the upstream
end of at least one flow passage-way 31b extending in the
second condensing heat exchanger 16'b and the upstream end
of which is connected through an outer duct to the phase se-
parator 26 already described with reference to Figure 3.
In the closed circuit 3 of the auxiliary or heavy re-
frigerating fluid, the compressor se-t 32 here consists suc-
cessively, in the direction of flow of the refrigerating
fluid, of a first compressor 32a1, of a second compressor
32a2 and of a third compressor 32b forming a like number of
compression stages and which may be operatively driven as in
the embodiments of the foregoing figures either separately
by individual prime movers, respectively, or at least two or
all of them may be driven by one single common prime mover
while being thus mechanically coupled to one another through
their respec-tive shafts. Moreover as in the embodiments pre-
viously described and shown the compressor sets 12 and 32
for the main and auxiliary refrigerating fluids, respective-
ly, may be driven either separately by individual prime mo-
vers or both sets or at least two compressors belonging to
each set, respectively, may be driven by a common prime mo-
ver while being thus mechanically coupled to each other.
The outlet or delivery port of the first compressor 32a1
is connected by means of a duct 60 to the suction port of the
second compressor 32a2 through an intermediate or inter-stage
cooler 34' which is advantageously o~ the type having an ou-
ter cooling fluid consis-ting for instance of water or air.
26
~ 6
The second compressor 32a~ ~nd the third compressor 32b here
are comparable to the first and second compressors 32a and
32b, respectively, o~ the circuit diagram according to Figu-
re 3, so that their mutual connecting configuration is simi-
lar to that shown Dn Figure 3.
The outlet of the after-cooler 38 is connected to the
upstream end of ~t least one flow passage-way 42a contained
in the first condensing heat exchanger 16'a and the down-
stream end of which is connected through an intermediate duct
37' to the upstream end of at least one flow passage-way 42b
located in the second condensing heat exchanger 16'b and the
downstream end of which is connected through an outer duct
43b to ~he inlet of a hydraulic expansion turbine 44b (the
shaft oi which is possibly coupled mechanically to a rotary
machine 45b). The outlet of the turbine 44b is connected by
means of a duct 46b (and possibly through an additional ex-
pansion valve 50b) to the upstream end of at least one pas-
sage-way 47b contained in the second condensing heat exchan-
ger 16'b and the downstream end of which is connected through
an outer duct 49b to the suction port of the first compressor
32a1. As a matter o~ fact, the intermediate duct 37' is bi-
furcated because at an intermediate branch point 61 thereof
is connected a branch duct 43a connecting this point to the
inlet of a cryogenic hydraulic expansion turbine 44a (the
shaft o~ which is possibly coupled mechanically -to a rotary
machine 45a). The outlet of this turbine 44a is connected by
a pipe-line 46a possibly through an additional expansion
valve 50a to the upstream end of at least one passage-way 47a
extending in the first condensing heat exchangers 16'a and
the downstream end of which is connected at the outlet 48a o~
said exchanger through an outer duct 49a to the suction port
of the second compressor 32a2 while joining the duct 60 at a
common branch point 62.
The outstanding features of the operation of this system
according to Figure 4 are then the following :
~1~289L6
27
- In the circuit 1, the gas to be liquefied GN, fed
through the duct 4 for instance at a temperature of about
+20C and at a pressure of about 45 bars flows through the
passage-way 28 of the cooling device 27 to be preliminari-
ly cooled therein through heat exchange with the main or
light refrigerating fluid for instance down to a temperature
of about -70C and at a pressure of about 44 bars. The gas
thus cooled then flows possibly through a gas processing
apparatus ~0 which for instance will remove its heaviest
components therefrom before flowing through the heat exchan-
ger ~ to be successively liquefied and then sub-cooled there-
in for instance down to a temperature of about -160C at a
pressure of abou-t 41 bars. When leaving t ~ heat exchanger
the sub-cooled liquefied gas is successively expanded and
then stored as previously described.
- In the closed circuit of the main or light refrigera-
ting fluid 2, the latter, issuing in the gaseous state from
the after-cooler 15 for instance at a temperature of about
+30C and at a pressure of about 31 bars flows th~ ugh the
flow passage-way 31a of the first condensing heat exchanger
16'a to be partially liquefied therein through heat exchange
with the auxiliary or heavy refrigerating fluid. The
main refrigerating fluid thus partially condensed leaves the
first condensing heat exchanger 16'a for instance at a tem- --
perature of about -30C and at a pressure of about 30 bars
to be fed to the separator 51 performing the separation of
its gaseous and liquid phases, respectively. Its liquid pha-
se then flows through the flow passage-way 53 of the heat
exchanger 27 to be sub-cooled therein for instance down to a
~0 temperature of about -70C and at a pressure of about 28
bars and then it flows through the cryogenic hydraulic tur-
bine 55 to be expanded therein (thereby inducing or sustain-
ing the continuous rotary motion of the turbine possibly to-
gether with attendant driv~ of the rotary machine 56) while
having thus for instance its temperature lowered to about
28
-75C and its pressure lowered to about 3.2 bars. This liquid
phase thus expanded possibly undergoes an additional expan-
sion by flowing through the (optional~ expansion valve 58 and
then joins the vaporized portion of the main refrigerating
fluid leaving the heat exchanger 3 through the outlet port 24
before the total fluid flow rate passes through the passage-
way 29 of the heat exchanger 27 to vaporize fully therein
~efore being drawn in again and recompressed by the compres-
sor set 12. The gaseous phase separated in the separator 51
flows through the flow passage-way 31b of the second conden-
sing heat exchanger 16'b to be partially liquefied therein
through heat exchange with the auxiliary refrigerating fluid
so that it issues from this second heat exchanger 16'b for
instance at a temperature of about -70C and at a pressure of
about 29 bars to reach the separator Z6 already descrihed
previously ; thus the subsequent evolution of this second
portion of the main refrigerating fluid would correspond to
what has already been described with reference to the embodi-
- ment shown on Figure 3. It should however be pointed out that
the sub-cooled liquid fraction of the main refrigerating
fluid which flows through the hydraulic turbine 19b enters
the latter for instance at a temperature of about -140C and
at a pressure of about 28 bars to flow out there~ in the ex
panded condition for instance at a temperature of about
-143C and at a pressure of about 3.5 bars whereas the sub-
cooled liquid fraction of the main refrigerating fluid which
flows through the hydraulic turbine 19a enters the latter for
instance at a temperature of about -1600C and at a pressure
of about 27 bars to ~low out thereof in the expanded state
for instance at a temperature of about -163C and at a pres-
sure of about 2.7 bars ; the portion of the main refrigera-
ting fluid to be totally vaporized in the heat exchanger 3
issues therefrom through the outlet port 24 preferably at the
same temperature (of about -75C) and pressure (of about 3.2
bars) as the expanded portion of main refrigerating fluid
coming through the duct 57 to mix therewith at the point of
~ 29
LZ846
junction 59. The total main refrigerating fluid then flows as
already stated through the passage-way 29 of the heat exchan-
ger 27 to be fully vaporized therein while streaming therein
. the direction opposite to the direction of circulation of the
fluids in the passage-way 28 and the flow passage-way 53,
respectively, of the same exchanger 27 while being in heat
exchange therewith in order to cool the gas to be liquefied
in the passage-way 28 and to sub-cool the liquid fraction of
the main refrigerating fluid in the flow passage-way 53. The
10 vaporized total refrigerating fluid thus reheated in the heat
exchanger 27 for instance up to a temperature of about +10C
a-t a pressure of about 3 bars is drawn in again and recompres-
sed by the compressor set 12. It is thus found that in this
embodiment according to Figure 4 the main refrigerating fluid
is split into two portions the larger one of which flows
through the heat exchanger 3.
In the closed circuit of the auxiliary or heavy refrige-
rating fluid 3, the compressed auxiliary refrigerating fluid
issuing in the fully condensed or liquid state from the con-
20 denser 38 for instance at a temperature of about +30C and ata pressure of about 40 bars flows through the flow passage-
way 42a of the first heat exchanger 16'a to be sub-cooled
therein for instance down to a -temperature of about -30C and
at a pressure of about 39 bars. When leaving th~ first heat --
exchanger 16'a the main refrigerating fluid thus sub-
cooled once is divided up at the point 61 of the duct 37'
into two portions. One of these two portions flows through
the hydraulic turbine 44a to be expanded therein (thereby in-
ducing or sustaining a continuous rotary motion of the turbi-
30 ne possibly together with attendant drive of the rotary ma-
chine 45a) while having thus for instance its tèmperature
lowered to about -33C and its pressure lowered to about 10.2
bars ; this portion thus expanded possibly undergoes an
additional expansion through the (optional) expansion valve
50a before flowing through the passage-way 47a of the first
- ~o
heat exchanger 16'a to keep vaporlzing therein by circulating
in a direction opposite to the common direction of flow of
the respective fluids in the flow passage-ways 31a and 42a,
while being ln heat exchange therewith so as to partially li-
quefy the main refrigerating fluid in the flow passage-way
31a and to sub-cool the liquid auxiliary refrigerating fluid
in the flow passage-way 42a. The vaporized portion of the
auxiliary refrigerating fluid thus reheated in the first heat
exchanger 16'a leaves the latter for instance at a temperature
of about +25C and at a pressure of about 10 bars to be drawn
in again by the second compressor 32a2. The other portion of
the liquid auxiliary refrigerating fluid in the duct 37', al-
ready sub-cooled once then flows through the ~low
passage-way 42b o~ the second heat exchanger 16'b to be still
further sub-cooled therein for instance down to a temperature
of about -70C and at a pressure of about 38 bars before
~lowing through the hydraulic turbine 44b for being expanded
therein (thereby inducing or sustaining the continuous rotary
motion of the turbine possibly together with attendant drive
of the rotary machine 45b) while having thus for instance its
temperature lowered to about -73C and its pressure lowered
to about 2.2 bars. This portion thus expanded possibly under-
goes an additional expansion by flowing through the (optional)
expansion valve 50b and then flows through the passage-way
47b of the second heat exchanger 16'b to be fully vaporized
therein while streaming therein in a direction opposite to
the common direction of circulation of the fluids in the flow
passage-ways 31b and 42b, respectively, while being in heat
exchange therein with these fluids, so as to partially lique-
fy the main refrigerating fluid in the flow passage-way 31b
and to additionally sub-cool the liquid auxiliary refrigera-
ting fluid in the flow passage-way 42b. This vapori~ed por-
tion of the auxiliary refrigerating fluid thus reheated by its
flow through the second heat exchanger 16'b leaves the passa-
ge-way 47b of the latter through the outlet port 48b while
2t~4~
being for instance at a temperature o~ about -33C and at a
pressure of about 2 bars to reach the duct 49b at the suction
port of the first compressor 32a1 in order to be recompressed
therein in the gaseous state and then cooled by flowing
through the intermediate cooler 34' before joining at the
point of junction 62 the vaporized portion of the auxiliary
refrigerating fluid issuing from the first heat exchanger
16'a through the duct 49a, the total flow rate of the gaseous
auxiliary refrigerating fluid thus restored being then drawn
in again and recompressed by the second compressor 32a2. The
auxiliary refrigerating fluid thus compressed in the gaseous
state and then partially liquefied in the condenser 34 issues
from the latter for instance at a temperature of about ~-30C
and at a pressure of about 20 bars before being fed into the
separator 35.
It should be pointed out that at least one or each one
of the passage-ways29 (circuit 2) and 47a, 47b (circuit 3)
~here the refrigerating fluids involved are fully vaporized
in the confined state could be replaced by a jet-producing
spray distribution member of a type comparable to the member
21a or 21b.
The system shown in Figure 5 makes use again of a single
closed circuit or refrigeration cycle 2 for a single refrige-
rating fluid which is here divided into four fractional por-
tions respectively cooled previously through heat exchange
with parts o~ themselves in the vaporized state a~d only the
last fractional portion of which is used for the liquefaction
and subsequent sub-cooling of the gas to be liquefied. The
circuit 1 of the gas to be liquefied as well as that portion
of the circuit 2 of the refrigerating fluid which is used for
the preliminary cooling, the liquefaction and the sub-coo-
ling of the gas to be liquefied are substantially equivalent
to the corresponding portions~ respectively, of the circuits1
and 2 shown on Figure 3 in particular with respect to the
heat exchangers 3 and 27. The outstanding particular features
of the circuit of refrigerating fluid 2 are the following.
32
~L4;~ 6
The compressor set 12 for the gaseous refrigerating
fluid consists of three compressors ~2a1, 12a2 and 12b, res-
pectively, forming a like number of successive compression
stages and which may be driven either separately through in-
dividual prime movers or collectively ~or at leastt~o or all
of them by means of one single common prime mover, the col-
lectively driven compressors being then mechanically coupled
to each other. The outlet or delivery port of the second
compressor 12a2 is connected through a pipe-line 63 to the
inlet of a condenser 64 which advantageously is of the type
operating with an outer cooling fluid consisting for instance
of water or air and the outlet of which is connected to a pha-
se separator 65. The gaseous phase collecting space of the
separator 65 is connected through a pipe-line 66 to the suc-
tion port of the third compressor 12b the outlet or discharge
port of which is connected through ~ duct 67 to the inlet of
a condenser 68 the outlet of which is connected to a phase
separator 69. The liquid phase collecting space of the sepa-
rator 65 is connected through a duct 70 to the suction port
of a circulating and accelerating pump 71 the delivery port
of which is connected to the delivery duct 67 of the third
compressor 12b at an intermediate branch point 72 located
upstream of the condenser 68. There are moreover provided two
successive condensing heat exchangers 73a and 73b for the re-
frigerating fluid which may consist either of two physically
dis~inct units or be integrated into a same body 7~ forming
an enclosing shell or ca~ing common to both aforesaid conden
sing heat exchangers (as shown on Figure 5).
The condensing heat exchanger 73a contains at least two
flow passage-ways 74 and 75 extending in generally parallel
relation to a same direction. The upstream ends o~ the flow
passage-ways 74 and 75 are connected respectively through
ducts 76 and 77 to the gaseous phase collecting space and to
the liquid phase collecting space of the separator 69. The
downstream end of the flow passage-way 75 is connected through
a pipe-line 78 to the inlet of a cryogenic hydraulic expansion
33
~ 6
turbine 79 (having its shaft possibly coupled mechanically
to a rotary machine 80) located outside of the heat e~chan-
ger 73a. The outlet of the turbine 79 is connected by a pi-
pe-line 81 possibly through an additional expansion valve
82 to a distribution member 83 placed for instance in the
shell o~ the heat exchanger 73 towards the end of the heat
exchanger 73a on the side of the downstream ends of the flow
passage-ways 74 and 75. This distribution member is for ins-
tance of the jet-producing spray distributor type pointing
towards the flow passage-ways 74 and 75 and opening directly
into the inner space of the shell of the heat exchanger 73a.
The downstream end of the flow passage-way 74 is connected
-through a duct 84 to a phase separator 51' positioned outsi-
de of the heat exchangers 73 and the gaseous phase and liquid
phase collecting spaces of which are connected respectively
thn~ t'le du~ 85 and 86 to the upstream ends of at least two
flow passage-ways 87, 88 extending within the heat exchanger
73b in general parallel relation to a common direction. The
downstream end of the flow passage-way 87 is connected
through a pipe-line 89 to the outer phase separator 26 al-
ready described previously with respect to its corresponding
downstream mounting configuration. The downstream end of the
flow passage-way 88 is connected through a pipe-line 90 to
the inlet of a cryogenic hydraulic expansion turbine 91 (ha-
ving its shaft possibly coupled mechanically to a rotary ma-
chine 92) which is outside of the heat exchanger 73b. The
outlet of the turbine 91 is connected by a pipe-line 93 pos-
sibly through an additional expansion valve 94 to a distri-
bution member 95 for instance located within -the heat exchan-
ger 7~b towards that end thereof which is placed towards thedownstream ends of the flow passage--ways 87 and 88. ~his
distribution member 95 is for instance of the jet-producing
spray distributor type oriented towards the flow passage-ways
87 and 88 and opening into the inner space of the shell 73
common to both heat exchangers 73a and 7~b and the inner spa-
ce of which th~s is common to both of the latter. The exchan-
34
2~4~6
ger 73 instead of being of the type provlded with a nest,cluster or bunale of coiled tubes, may be of the plate cons-
truction type~ ~ such a case one or each one of the distri-
bution members 83 and 95 may consist of at least one passa-
ge-way extending in substantially parallel relation ~ the
flow passage-ways 74, 75 or 87, 88 which are associated
therewith.
The common inner space defined by the shell 73 communi-
cates at its end located towards the upstream ends of the
flow passage-ways 74 and '75 through a duct 96 with the suc-
tion port of the second compressor 12a2. The duct 25, ex-
tending from the outstream end of the coil of tubing or pi-
ping 29 of the heat exchanger 27 leads to the .~uction port
of the first compressor 12a1 the outle-t or delivery port of
which is also connected to the suction port of the second
compressor 12a2 by means of a duct 97 and through an inter-
mediate or inter-stage cooler 98 for instance of the type
operating with an outer cooling fluid consisting for instan-
ce o~ water or air and the outlet of which is connected to
the duct 96 at a branch point 99 thereof.
The operation of the circuit 1 of gas to be liquefied
is similar to that which has been desc:ribed with reference
to Figure 3 but with the following different numerical va-
lues of temperature and pressure by way of example : -
- at the inlet of the duct 4, the gas to be liquefied
GN is at a temperature of about +20C and at a pressure of
about 45 bars ;
- at the inlet of the heat exchanger 3 this gas is at a
temperature of akout -60C and at a pressure of about 44 bars;
- at its outlet of the heat exchanger 3 the sub-cooled
liquefied gas is at a temperature of about -160C and at a
pres~ure of 41 bars.
The outstanding operating ~eatures of the cycle of re-
frigerating ~luid 2 are the following : the t.otal gaseous re-
frigerating fluid is drawn in by the second compressor 12a2
to be recompressed in the gaseous state and then partially
lique~ied in the condenser 64 for instance at a temperature
~ 6
of about ~30C and at a pressure of about 20 bars. This par-
tially liquefied fluid then undergoes a phase separation
within the separator 65 ; its gaseous phase is drawn ~n by
the third compressor 12b to be recompressed in the gaseous
state whereas its liquid phase is drawn in and compressed in
the liquid state by the pump 71 which will move it to join
at 72 the compressed gaseous phase delivered by the compres-
sor 12b. This mixture of gaseous and liquid phases, respec-
tively, then flows through condenser 68 to undergo an addi-
10 tional partial liquefaction therein for instance at a tempe-
rature of about + 30C and at a pressure o~ about 35 bars
before undergoing a new phase separation in the separator 69.
The li~uid phase thus separated flows through the flow passa-
ge-way 75 of the first heat exchanger 73a to be sub-cooled
therein through heat exchange with a vaporized portion of
itself whereas the gaseous phase flows through the flow pas-
sage-way 74 of the same heat exchanger to be cooled therein
until partial lique~action through heat exchange with said
same vaporized portion. The sub-cooled liquid phase issuing
20 from the flow passage-way 75 for instance at a temperature of
about -20~C and at a pressure of about 34 bars flows through
the hydraulic turbine 79 to be expanded therein (thereby in~u-
cing or sus~aining ~ continuous rotary motion of the turbine
possibly together with attendant drive of the rotary machine --
80). The fluid thus expanded possibly undergoes an additional
expansion through the (optional) expansion valve 82 before
reaching the distribution member 83 of the heat exchanger 73a
wherein it keeps vaporizing while streaming in the direction
opposite to the common direction of circulation of the res-
30 pective fluids in the flow passage-ways 74 and 75 so as to
provide through heat exchange with these fluids ~or thè par-
tial liquefaction of the gaseous phase in the flow passage-
way 74 and for the sub-cooling of the liquid phase in the flow
passage-way 75.
~6
~2~6
The partially li~uefied fraction issuing from the flow
passage-way 74 for instance at a temperature of about -15C
and at a pressure of about ~5 bars undergoes in the separa-
tor 51' a separation of its respective gaseous and liquid
phases which then flow through the flow passage-ways 87 and
88, respectively, of the second heat exchanger 73b. In the
flow passage-way 87 the gaseous phase is partially liquefied
and in the flow passage-way 88 the liquid phase is sub cool-
ed through heat exchange with a vaporized portion of the
latter. The sub-cooled liquid fraction leaves the flow pas-
sage-way 88 for instance at a temperature of about -60C and
at a pressure of about 33 bars to thereafter flow through
the hydraulic turbine 91 for being expanded therein (thereby
inducing or sustaining the continuous rotary motion of the
turbine possibly together with the attendant drive of the
rotary machine 92). The fraction thus expanded, having for
instace its temperature lowered to about -630C and its pres-
sure lowered to about 7.2 bars possibly undergoes an addi-
tional expansion through the (optional) expansion valve 94
before reaching the distribution member 95 of the exchanger
73b where it keeps vaporizing while streaming in the direc-
tion opposite to the common direction of circulation of the
respective fluids in the flow passage-ways 87 and 88, in or-
der to carry out a heat exchange sub-cooling the liquid
fluid in the flow passage-way 88 and partially liquefying
the gaseous fluid in the flow passage-way 87. The fraction
of refrigerating fluid thus vaporized in the heat exchanger
73b then flows into the exchanger 73a for mixing therein
with the vaporized portion of the re~rigerating fluid. All
the vaporized portions of the refrigerating fluid origina-
ting from the liquid phases, respectively, separated in the
separators 69 and 51' and thus reheated through heat exchan-
ge with the flow passage ways 74, 75 and 87, 88 leave the
heat exchanger 73 through the duct 96 for instance at a tem-
perature of about ~20C and at a pressure of about 6.8 bars.
37
~ 6
The partially llquid fraction in the flow passage-way
87 leaves the latter through duct 89 for instance at a tem-
perature of about -60UC and at a pressure of about 33 bars
to reach the phase separator 26 and thereafter evolve as
previously described in particular with reference to the
embodiments according to Figures 2 to 4 but with different
numerical temperature and pressure values given by way of
example only hereinafter :
- at the inlet of the turbine 19b the sub-cooled liquid
is at a temperature of about -130C and at a pressure of
about 31 bars whereas at the outlet of this turbine the ex-
panded fluid is at a temperature of about -133C and at a
pressure of about 1.8 bar ;
- at the inlet of the turbine 19a the sub-cooled liquid
fluid is at a temperature of about -160~C and at a pressure
of about 30 bars whereas at the outlet of this turbine the
expanded fluid is at a temperature of about -163C and at a
pressure of about 2 bars ;
- the vaporized fluid issuing from the port 24 of the
casing of the heat exchanger 23 is at a temperature of about
-65C and at a pressure of about 1.5 bar whereas at its out~
let from the passage-way 29 of the heat exchanger 27 it is
at a temperature of about +10C and at a pressure of about
1.3 bar in the duct 25 for being drawn in again under these
conditions and recompressed by the first compressor 12a1.
The fraction of the gaseous refrigera-ting fluid thus
compres.sed in the first compressor 12a1 is delivered through
the intermediate or inter-stage cooler 98 wherefrom it issues
substantially at the same temperature and pressure as the
fraction of the gaseous fluid fed by the duct 96 and then
both fractions will join at the point 99 so that the total
gaseous refrigerating fluid is thus drawn in again by the se-
cond compressor 12a2.
The various embodiments described and shown on Figures 1
to 5, respectiv~ly, of the drawings obviously are part of the
invention on account o~ their particular structures.
The invention is of course not at all limited to the
embodiments described and shown which have been given by way
of illustrative examples only. In particular it comprises
all the means constituting technical equivalents of the
means described as well as their combinations if same are
carried out according to its gist and used within the scope
of the appended claims.
